<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<div id="app">
  <h2 :style="{fontSize:finalSize, color:finalColor}">{{message}}</h2>
  <h2 :style="getStyles()">{{message}}</h2>
</div>

<script src="./js/vue.js"></script>

<script>
    const app = new Vue({
        el:'#app',
        data:{
            message:'Hello World',
            finalSize:'100px',
            finalColor:'red'
        },
        methods:{
            getStyles:function(){
                return {fontSize: this.finalSize, color: this.finalColor, background:'grey'}
            }
        }
    });
</script>
</body>
</html>